Gas analysis apparatus



May 13, 1941. AfE. KROGH ET AL 2,241,555

GAS ANALYSIS APPARATUS I Filed May 22, 1937 s Sheets-Sheet 1 Irv/anions;

A TTORNEY M 19411- A. E. KROGH ETAL 5 2,241,555

' GAS ANALYSIS APPARATUS Filed May 22, 1937 s Sheets-Sheet 2 FIG. 2.

Inventors.

A 5' I2, J 2??? Pi l rafi RA ATTORNEY May 13, 1941. A. E. KROGH ETAL GASANALYSIS APPARATUS Filed May 22, 1937 3 Sheets-Sheet 3 ATTORNEY PatentedMay 13, 1941 UNITED s'm' rzs PATENT OFFICE GAS AN ALYSIS APPARATUS AnkerE. Krogh and Joseph P. Vollrath, Philadelphia, Pa., assignors to TheBrown Instrument Company, Philadelphia, Pa., a corporati n ofPennsylvania Application May [22, 1937, Serial No. 144,288

13 Claims.

One general object of the present invention is to provide an improvedmeans for gas analysis.

Another object of the invention is to provide a measuring instrumentwith simple ,and efiective means for-making measurements to one oranother of two different scales, accordingly as the value of thequantity measured is above or below a certain intermediate value in therange of variation to which the instrument is adapted to respond.

A more specific object of the invention is to provide for the analysisof the atmosphere in the furnace chamber of a heat treating or analogousindustrial furnace, by continuous measuremore or less analogous heattreating operations,

it is practically important to surround the tool or other steel or metalobject treated, by a fluid medium having certain specialcharacteristics, the nature of which depends upon the composition of thearticle treated, and the character,

burizing action, or to a decarburizlng action which does not necessarilyresult in scaling.

For some heat treatments of metals, it is possible to prevent oxidizing,carburizing, or .de-

carburizing troubles by immersing the article treated in' a suitablemolten metal bath. In general, also, it is theoretically possibletoconduct the treating operation with the article treated enveloped by agas inert to said article at the temperature range of the treatment.Nitrogen, for example, is suitably inert .for use in ordinary heattreatments of steel tools. It is not practically feasible, however, touse a special inert gas such as nitrogen for the bulk of the heattreatment and other operations, in which the composition of the furnacechamber atmosphere should be of a special characterf This has led to thedevelopment and exten sive use of special furnaces each includingproabove described may, and ordinarily will, include visions formaintaining a so-called controlled furnace atmosphere, by forming in, orintroducing into, the furnace chamber, the gaseous products formed bythe more or less complete combustion of some available combustible gas,such as Pyrofax, or ordinary, city gas, or some other available fuel gasnot too variable in its composition. The problem of operating such afurnace so as to secure the best practical results obtainable with it,has been difllcult in the past because of the practical inability of thefurnace operator to obtain the knowledge of the composition of thefurnace atmosphere, needed to enable the operator to repeatedlyestablish and maintain the particular furnace atmosphere givingsatisfactory results for the operator's particular purpose, and to avoidthe furnace atmosphere conditions which give unsatisfactory results.

Some of the difficulties which operators of the controlled atmospherefurnaces have experienced, result from the fact that the composition ofthe furnace atmosphere may vary as a result of disassociation of gases,and particularly the liberation of H2 from methane and ethane, as thefurnace temperature is raised, even though the composition of thecombustible gas supplied to form the furnace atmosphere and the gas andcombustion airratio be kept constant. Moreover, for many heattreatments, a furnace at' mosphere which is mildly reducing isdesirable, and such an atmosphere formed in the manner both CO and H2and may also include C02, all of which gases in slightly differentproportions, may also be found in furnace atmospheressufficientlyoxidizing to produce scaling.

There are various chemical methods of gas analysis theoreticallyavailable for use in determining the composition of the above mentionedcontrol furnace atmospheres, but the known chemical methods, availablefor laboratory work, are not practically suitable for the use of theoperators of controlled atmosphere furnaces. We have discovered,however, that it is practically possible for the furnace operators toobtain immediately useful and valuable knowledge concerning thecomposition of the above 66 mentioned controlled furnace atmospheres, by

measuring the thermal conductivity of the gaseous mixture constitutingsaid atmosphere with the apparatus which we have devised for thepurpose. That apparatus is characterized in particular by provisions forchanging the measurement scale, .as the thermal conductivity varies Ifrom one side or the other of a certain intermediate value, so as tofurnish suitably sensitive and accurate measurements both when thethermal conductivity of the furnace atmosphere is relatively low andwhen it is relatively high.

In the preferred practical embodiments of our invention, we take intoaccount, and give effect to, the significance of appreciable amounts ofCO2 and H2 inthe furnace atmosphere. The thermal conductivity of CO2 isless than sixtenths that of air. The thermal conductivity of H2 isnearly seven times that of air. Oxygen, nitrogen and carbon monoxidehavethermal conductivities differing only a few-percent from that ofair. In general, when a furnace atmosphere of the kind above mentionedhas a thermal conductivity less than that of air, there has beensubstantially complete combustion of the combustible elements suppliedto form the atmosphere, and the difierence between the thermalconductivities of the furnace atmosphere and air is proportional to andforms a measure of the CO2 content of theatmosphere. On the other hand,when the thermal conductivity of such a furnace atmosphere issignificantly above that of air, the difference will be due to thepresence of H2 in the atmosphere, and will constitute a measure of thehydrogen content of the atmosphere.

In the preferred practical embodiment of our invention, we divide thedeflection range of the measuring instrument into substantially equalhigh and lowjdeflection sections, separated by a narrow intermediatesection,- and provide means for changing the scale of the measurementssoa part of the apparatus diagrammatically shown in Fig. 1;

Fig, 4 is a perspective view of a portion vof a recording millivoltmeter which may be used in lieu of the potentiometer instrument shown inFigs. 1 and 2, to record furnace atmosphere variations;

Fig. 5 is an elevation of a switch mechanism included in the instrumentshown in Fig. 4;

Fig. 6 is a diagram of a portion of a measuring circuit arrangementincluding different test gas cell resistors for use in differentportions of the measuring range; and

Fig. 7 is a view illustrating a portion of an instrument includingchangeable gear means for maintaining difl'erent measuring scales indifierent portions of the measuring range.

I In Fig. l, we have illustrated diagrammatically a preferred embodimentof the present invention used in analyzing .the atmosphere in a fur-,

nace A, and in continuously indicating and recording the analysisresults, The furnace A shown trolled, to obtain the best heat treatmentresults.

that the low deflection section may be effectively utilized-indetermining the CO2 content of the atmosphere, through the normal rangeof variaand so that the high deflection section may be effectivelyutilized in measuring the hydrogen content of the atmosphere, which mayvary from tion in that content from zero up to about 14%,

zero up to 100%, though in the normal intended use of most suchfurnaces, the hydrogen content will be substantially less than 100%.Those skilled in the art will understand that in maintain a controlledfurnace atmosphere in any particular furnace for any one particular heattreating operation, the furnace atmosphere composition should bemaintained approximately constant, and may be so maintained by the useof the measuring apparatus which'we have devised.

The various features of novelty which charac terize our invention arepointed out with pantieularity in the claims annexed to and forming apart of this specification. For a better under- "the use of anyparticular combustible gas to standing of the invention, however, itsadvan-- use of the present invention in connection with a treatingfurnace of well known commercial type;

Fig. 2 s a partial front elevation of a recording potentiometerinstrument included in the apparatus shown in Fig. 1; V

Fig- 3 is a diagram illustrating a preferred measuring circuitarrangement for use in and as As shown, the metal tools or other partstreated are supported in the furnace chamber A, on a refractory supportA, which extends across the chamber, and about which the furnace chamberatmosphere may circulate. Within the chamber are resistance bars orother suitable electric heating elements A A suitable atmosphereforming, fuel gas is burned in a precombustion chamber A, formed in therefractory housing of the chamber A, and from which products ofcombustion pass through a port A into the throat A of the chamber A. Theport A is in the form of a narrow slot in the bottom wall of the throat.The combustion occurring in the chamber A may be regulated to providegaseous products of combustion having the composition desirablymaintained in the chamber A. Those products are discharged through theport A in a'sheet-like jet, forming a curtain extending across thethroat A Such a cur-tain is effective to prevent atmospheric air frompassing into the furnace chamber through the peephole A", shown asformed in the door A normally closing the outer end of the throat, andis also effective to prevent the influx of air when the door is opened.In the furnace conventionally illustrated, means are provided forincreasing the volume of products formed in the chamber A and dischargedacross the throat A, during each period in which the door A is displacedfrom its normally closed position.

In addition to its curtain forming effect, the combustion gasesdischarged through the port A displace objectionableatmospheric'constituents which may be within the chamber A at thebeginning of a heat treating operation. Excess products of combustionescape from the chamber A through its vent outlet A. As shown, gas, andair for its combustion, are supplied to the chamber A through pipes Aand A, respectively, and A and A represent gages associated with thepipes A and A", respectively to, provide measures of the rates of flowthrough the pipes. and guidance for the adjustment of valves controllingsaid rates of flow, so as to insure the 1desired composition for theproducts of composiion.

The presentinvention is not limited to use in connection with a furnacesimilar in type or kind to the furnace A, and the latter forms no partof the present invention, but the use to which such a furnace A isordinarily put is one in which the present invention may be used withgreat advantage, so as to permit a highly eflicient use of the specialprovisions made to control atmospheric conditions in the furnace chamberA.

In the form shown in Fig. 1, the gas analyzing apparatus associated withthe furnace A comprises an aspirator C constantly moving a stream of gasfrom the furnace chamber A through the test cell or cells of a thermalconductivity comparison cell structure B, along a flow path comprising asampling tube D, conduit sections E and E, and gas conditioning elementsF, F, and

In many cases the exhaust gases from the equipment illustrated in Fig. 1are obnoxious, inflammable or otherwise undesirable and under suchcircumstances we may dispense with the. aspirator and provide acontinuous pipe line from the outlet of the cell B back to the furnaceA. A circulating pump may then be inserted in the said pipe line fordrawing gases through connections D, E, F, F, E, F, F, B, F and the pumpback into the furnace. This method is desirable also from the standpointof the maintenance of the desirable gas pressure and flow.

The comparison cell structure B can be of any usual or suitable type,and in particular it may, and will be herein assumed to be, of the typedisclosed in the Harrison Patents 1,818,619 granted August 11, 1931, andNo. 1,829,649 granted October 27, 1931, in which two test gas and twostandard gas cells of cylindrical form, are arranged side by side in aone-piece metallic cell block, an electric current carrying resistorbeing arranged in each cell. In using such a cell structure in thearrangement of Fig. 1, the test gas withdrawn from the chamber A, ispassed in separate parallel streams continuously through the two testgas cells, and the standard gas in the other two cells, may be airsealed in those cells. The two test cell resistors BR and the twostandard cell resistors b1 are connected in a suitable measuringcircuit, a preferred form of which is shown in Fig. 3, so that thechanges in relative resistance of the resistors in the test and standardgas cells, due to differences in their temperatures produced bydifferences in the thermal conductivities of the test and standardgases, create potential changes in the circuit which can be measured.

In order that the composition of the gas in a heat treating furnacechamber such as the chamber A', may be determined with suitableaccuracy, it is necessary to avoid contamination or modification in thecomposition of the gas as a result of the contact of the gas, while at ahigh temperature, with the walls of the flowpath. To this end, thesampling tube D may well be made of the refractory ceramic materialknown as sillimanite, and the adjacent section of the flowpath, for thelength of 20 feet or so required to cool the gas down approximately toan atmospheric' temperature, may well be in the form of a lead tube.

Accuracy of ,measurement requires that the test gas should pass throughconditioning means by which the gas is brought to a certain standardcondition, in respect to temperature, moisture content, and freedom fromimpurities, before entering the test cells, and that the generaltemperature of the test cell structure should be kept approximatelyconstant. To these ends, the gas conditioning means illustrated in Fig.1 comprise a gas cooler or condenser F, a gas dryer F, and a gascleaning filter F Backflow of air into the test cells through theaspirator C is prevented by a glycerin seal F Liquid separating from thegas in the condenser F is received in a receptacle F providing a liquidseal between the atmosphere and the gas space in the condenser. Thecondenser and cell structure B are cooled by water supplied by a pipe Gto a cooling space in the condenser F, from which the water passesthrough pipe connections G, a cooling space in the cell structure B, andpipe portions G and G to the aspirator C, in which the water serves asthe motive fluid for creating a suitable and suitably constant suctionat the outlet of the seal F The water, and the gas drawn by it into theaspirator C, escape from the latter through downwardly directeddischarge pipes C and C the drip from which is received by a sumpconnection C The cable sections H, H, H and H shown in Fig. 1, includethe conductors employed to operatively interconnect the cell resistorsinthe comparison cell structure B, the recording potentiometerinstrument I, a control panel K, including a milliameter K and arheostat K for maintaining the proper energizing current flow throughthe cell resistors, and a source of current L. The latter may be abattery, or in some cases it may advantageously be an A. C. adapter,energized from an alternating current supply source and includingrectifying means and potentiometer or other means for impressingsuitable direct current voltages on the cell resistors and thepotentiometric instrument.

In the desirable cell resistor and measuring circuit arrangement showndiagrammatically in Fig. 3, the two test cell resistors BR. of the cellstructure B, are included in opposing arms of a Wheatstone bridge I),each of the other two arms of which include a corresponding one of thetwo standard gas cell resistors b1. As shown, one of the two energizingjunctions, l, of the bridge I). is the point of engagement of acalibrating switch arm b with a slide wire resistance b The latterconnects one resistance BR in one, and one resistance hr in the other ofthe two branches of the bridge circuit connecting the bridgeenergization junction 1, to the second bridge energization junction 2.The bridge energizing source of current, shown in Fig. 3 as a batteryLA, the control panel ammeter K and rheostat K and the switch arm b areconnected in series with one another between the bridge energizingjunctions l and 2.

In operation, the rheostat K is adjusted from time to time as requiredto maintain the bridge energizing current flow indicated by the amineterK at a predetermined normal value. The switch arm b is adjusted alongthe slide wire resistance b for calibration purposes, when and as maybedesirable to insure the proper distribution of flow through the twobridge branches connecting the junctions I and 2, when the various cellresistors are subjected to standard temperature conditions. On a changein composition producing a change in the thermal conductivity of thetest gas, the resultant change in the resistance of the test cellresistors BR,

, produces changes in opposite directions in the rent flow in a circuitbranch which connects resistances 5 and 6, connected in series with oneanother. Normally the various resistors BR and Dr may be separatelyadjusted" for purposes of circuit calibration, but such calibratingadjustments may be effected, if desired, by manipulation of a resistorBr inserted in the conductor By way of illustration it is noted that thepotential of battery LA may desirably be 6 volts and thatcorrespondingly suitable resistance values for the various bridgeresistors may be as follows:

- Ohms The instrument I includes provisions for measuring either thepotential drop in the resistance 5, or the total potential drop in thetwo resistances 5 and 6, accordingly as the thermal conductivity of thetest gas is above or below a certain standard which is predetermined,and which, for the ordinary use of the apparatus shown, is the thermalconductivity of the standard gas. Whether the instrument I is incondition to measure the potential drop through the resistance 5, or thetotal potentialdrop through the resistances 5 and 6, depends uponwhether an instrument switch I, shown as a mercury switch, is

in its full line or in its dotted line positionshown in Fig. 3. Ashereinafter described, the switch is adjusted between its two positionsby movement in either direction of the recording pen carriage I' 'of theinstrument I through an intermediate portion of its range of movement.

The measuring circuit provisions of the instrument I in the form shownin Fig. 3 comprise a bridge 2'. The energizing junctions 8 and 9 of thebridge are connected by three circuit branches, one of which includesseries connected resistances llland H, their connectionpoint l2 forminga third junction of the bridge 2'. A second circuit branch connectingjunctions 8 and 9, includes a resistance l3 connecting the bridgejunction 8 to the fourth bridge junction IDA. The latter is connected tothe bridge junction 9 by resistances l4 and I5 in parallel with oneanother, the resistance l5 being the slide wire resistance of theinstrument I. The third circuit branch connecting the junctions 8 and 9,is the bridge ,the instrument I, a normally closed switch 1* andaconductor 20 to the middle terminal 2| of the switch I. When the switchI is in its'posi tion shown indotted lines in'Fig. 3, the terminal 2| isconnected by the mercury within the thebridge junctions 3 and 4, andincludes two bridge, and to the corresponding end of the resistance 6.When the switch I is in its full line position shown in Fig. 3, themercury in the switch container connects the middle switch contact 2| tothe left end contact 24. The latter is connected by a conductor 25 tothe point I at which the resistances 5 and 6 are connected to oneanother.

The switch I is the instrument calibrating switch. When the switch I isadjusted into its dotted line position shownin Fig. 3, the instrumentgalvanometer pointer I is disconnected from the switch I, and isconnected in series with a standard cell 26 and a calibrating resistance21 between the bridge junctions 9 and I2.

Whether the potential difference between the junctions 3 and 4 of thecell resistor bridge b will increase, or will decrease, as the thermalconductivity of the test gas increases, depends upon the relativeresistances of the bridge arms including the diiferent cell resistors,and is a matter of instrument design. If, for example, the resistance ofeach bridge arm including a cell resistor BR. is greater than theresistance of the bridge arm in series therewith for all temperatures ofthe resistors BR within the measuring range, the temperatures andresistances of those resistors, and the potential difference between thebridge junctions 3 and 4, will progressively decrease as the thermalconductivity of the test gas increases throughout the measuring range.As hereinafter appears, in a major contemplated field of use of theinvention, the possible increases in thermal conductivity of the testgas above that of the standard gas, are of much greater extent than thepossible decreases below the standard gas thermal conductivity. For suchuse, the apparatus collectively shown in Figs. 1, 2, and 3, mayadvantageously be arranged to tilt the switch I from its full lineposition into its dotted line position, or in the reverse direction asthe thermal conductivity of the test gas respectively decreases below orrises above a certain predetermined intermediate value.

The instrument I shown in Figs. 1 and 2 is a self-balancingpotentiometer of the commercial type known as the Brown potentiometer,and a form of which is shown in the Harrison Patent No. 1,946,280,granted Feb. 6, 1934. That instrument' comprises periodically actuatedrelay mechanism controlled by the deflection of the pointer I ofgalvanometer I on a change in the quantity measured, to angularly adjusta shaft I and thereby move the contact I along the slide wire resistanceI5 in the direction to rebalance the instrument and for a distance whichis dependent upon theextent of galvanometer deflection starting therebalancing operation. The angular adjustment of the shaft I is attendedby a corresponding angular adjustment of a helically grooved shaft 1 Therotation of'the latter adjusts a pen or marker carriage I longitudinallyof the shaft I with which the carriage is in threaded engagement.

The rotation of the shaft I thus moves the recorder carriagetransversely of a record sheet or strip which includes low and highconductivity sections M and M at opposite sides of a narrow centralsection M As the recorder carriage moves the recording element in onedirection or the other across the strip M the switch I is tilted fromits full line position into its dotted line position, or in the oppositedirection, accordingly as the carriagemovement is to the right or to theleft as seen in Fig. 2.

The mechanism through which the switch I is automatically actuated andthe form and character of the switch employed to do what is done by theswitch I in the circuit arrangement shown in Fig. 3, may differ widely,and are not of the essence of the present invention. The switch. I is asingle pole, double throw switch, and should be arranged to connect bothend contacts 22 and 24, to its contact 2| in each tilting operation sothat at least one of the two circuits through the switch is alwaysclosed. In practice the single switch I' may well be replaced bysimilarly actuated single pole switches, one controlling the circuitincluding the conductor 25, and the other the circuit including theconductor 23 of Fig. 3 in the manner in which those circuits arecontrolled by the switch I. The two single throw switches, when used arearranged for such overlapping action that neither will open until theother is closed.

The switch I of the instrument shown in Figs. 1 and 2, is actuated bythe rotation of the shaft 1, through mechanism devised by Coleman 3.Moore, and disclosed fully and in detail in the application for patentSerial No. 144,320, filed oi even date herewith. As shown herein, thatmechanism comprises a disc like actuating element 1 rotated by and inaccordance with the rotation of the shaft I and formed with a notch Iadapted to receive a projection I carried by a switch support I". Thelatter is mounted to oscillate about a supporting pivot I in fixedrelation with the instrument framework. In effect,

' the disc F with its notch 1 and the switch supside by side notcheddisc elements rotated at dif- 5 ferent angular speeds by the shaft 1',and having their individual notches brought into register-tocollectively form the notch I of the element 1*,

only when the pen-carriage marking-element is alongside the chartsection M Such a two disc arrangement permits an angular velocity of theelement I great enough to shift the switch I between its full and dottedline positions, on a comparatively small movement of the pen carriageI", so that the record chart strip M may be suitably narrow. 1

In the use of the apparatus shown in Figs; 1, 2, and 3, the pen carriagewill be displaced to the right or to the left as seen in Fig. .1, byincreases and decreases respectively, in the thermal conductivity of thetest gas, but ordinarily, the position of the pen carried along its pathof travel can be expected to directly furnish information of more directand immediate importance than the mere thermal conductivity of the gas.Under the operating conditions most usual in furnaces of the typeillustrated in Fig. 1, the measurements recorded on the record strip Mwill be thermal. conductivity -measurements obtained when the combustionof the gas supplied to the v ments on the chart strip M will bemeasurements-of the thermal conductivity of the test gas, obtained whenthat gas is reducing, and its thermal conductivity is high because ofits H2 content. In' consequence the scale portion 1 in .register withthe chart strip M may well be graduated and provided with scale marks toindicate the H2 percentage of the gas. Whether'the furnace chamber gasowes its reducing properties wholly or mainly to its H2 content, or insubstantial extent to its CO content, does not materially affect thevalue of the measurements given in terms of an assumed H2 content. Ifthat assumed content is higher or lower than the operator has foundsatisfactory for the work in hand, the operator will know thatconditions will be improved by respectively increasing or decreasing theratio of air to gas supplied to the chamber A.

Under the operating conditions assumed, in an intermediate portion ofthe range of thermal conductivity variation, where the H2 content of thegas mayvary only from a little less, to a little more than 1%, thethermal conductivity measurements do not give a reliable indication ofthe gas composition, and it is thus an advantage rather than adisadvantage to have the strip M 'wide enough to cover the saidintermediate range portion.

The above mentioned values for the various circuit resistances changedin accordance with the normal maximum H2 content to be encountered inthe furnace under measurement. For example, the values specified for theresistors 5 and 6' above renders the device suitable for H2 values ofthe order of 8% maximum. Maximum H2 values of 20% r 50% may be measuredby substitution resistors 5 and 6 as follows:

20% Hz 50% Hz Ohms Ohms

substantially constant instrument measuring sensitivity.

In Figs. 4 and 5, we have illustrated an embodiment of the invention inwhich'the measuring instr ent IA is not a potentiometer instrument, butis a simple deflecting type of galvanometer, which might have itsterminals connected to the junctions 3 and 4 of such a resistor cellbridge arrangement as is shown in Fig. 3, so that the galvanometerpointer. 1 would deflect in direct re-.

sponse to the potential difference between "said junctions. Theinstrument IA comprises a pivoted depressor I" having its pointerengaging portion normally above the path of deflection of thegalvanometer pointer I butperiodically lowered by the action of aconstantly rotating cam I" todepress the pointer I into a 'position inwhich it is supported by the record chart and its support. When thepointer is depressed it presses a carbon ribbon or other transfer medium1" against the chart and thereby makes a record of the pointer positionon the record chart strip. The latter is shown as comprising sections M,M, and M like those shown in Fig. 2.

As the pointer I? deflectsacross its mid posimay advantageously beresistance 1 tion, and is depressed by the action of the depressor I ittilts a switch member N about its pivot axis N in one direction or theother. When tilted counterclockwise, the switch member N engages aswitch-contact N, and when tilted clockwise, the switch member N engagesa switch contact N". The switch member N remains in each position intowhich it is tilted, until tilted into the other of its two positions asa result of a corresponding'change in the deflective position 'of thepointer I. As will be apparent, one terminal of the galvanometerincharacter shown in Fig. 2, the scale change may 7 be effected, byadjustment of the mechanism gas is reducing, in the'general manner inwhich the difl'erent scale measurements are effected with the apparatusof Figs. 1, 2, and 3.

To adapt it for another use, the instrument" IA is provided, with asecond switch 11, like and coaxial with the switch N. With its twoswitches N and 11., the galvanometer of the instrument IA may be used asthe galvanometer I in the circuit arrangement shown in Fig. 6. In thatarrangement the switches N and n are employed to change the measurementscale, by cutting one or the other of two pairs of test cell resistorsinto, and the other of the two pairs out of the measuring circuit, asthe switches are actuated. To this end in the arrangement shown in Fig.6, each test gas cell includes a resistor BR, and a second resistor theresistors BR. and In. In the bridge of Fig. 6,

however, the switch N is arranged to connect the bridge junctions I and3 either through the a corresponding resistor BR or v the adjacentresistor BR, and the switch n, similarly connects the bridge junctions 2and 4 either through the corresponding resistor BR or adiacent resistorBR. The switch member n is directly connected to the bridge junction 4.

'One terminal of the galvanometer I is' connected to the bridge junction4, and the other galvanometer terminal is connected to the bridgejunction 3 through an adjustable instrument As shown, the galvanometeris shunted by a resistance I The operationof the form of the inventionillustrated collectively by Figs. 4, 5, and 6, will be plainly apparentfrom what has already been said. As the galvanometer pointer I deflectsthrough its midpositionwith the result that the switches N and n aretilted in .one direction or the other, the extent of the deflection ofthe galvanometer pointer produced by a given extent of change in the.thermal conductivity of the test gas will be altered.

The measuring scale change which is eifected by one measuring circuitchange in Fig. 3, and by a different measuring circuit change in Fig. 6,may be effected in still difierent ways. In particular, it may beeffected by mechanical adjustments of the measuring apparatus. Thus, forexample, in an instrument of the general shown in Fig. 7, through whichthe angular speeds of the shafts I and I are related. As shown in Fig.2, the shafts I and 1 are geared together forsimultaneous andproportional rotative movements, by means including a shaft 1 connectedto the shaft I by bevel gears, and connected to the shaft 1 by spurgears I and I, respectively carried by the shafts 1 and 1 In Fig. 7, theshaft I carries a second spur gear I alongside the gear I and ofappreciably smaller pitch diameter. In Fig. 7, the gear I is connectedby a hub portion 1 to a larger gear I and the'two gears are splined foraxial movement on the shaft 1. Their movement in 'one direction bringsthe gear I? into mesh with and the gears I and I may be brought into Imesh by the energization' of an electro-magnet I. The latter isenergized by current supplied by battery LC, when the energizing circuitis closed by a. switch I", which may form part of a measuring instrumentlike that shown in Fig. 2, or that shown in Fig. 4, and be operatedgenerally as is the switch I of the first mentioned instrument or theswitch N or n of the second mentioned instrument.

While in accordance with the provisions of the statutes, we haveillustrated and described the best forms of embodiment of our inventionnow known to us, it will be apparent to those skilled in the art thatchanges may be made in the form of the apparatus and proceduredisclosed, without departing from the spirit of our invention as setforth in the appended claims} and that in some cases certain-features ofour invention may be used to advantage without a corresponding use ofother features.

Having now described our invention, what we claim as new and desire tosecure by Letters Patent, is:

ductivity and including adjustment means automatically actuated as saidpotential difierence attains a certain intermediate value, to adjustsaid apparatus for deflection of said element through approximately onehalf of its defiective range in response to the change in the thermalconductivity of said atmosphere produced by a 'variation in its hydrogencontent and for deflection of said element'through substantially all ofthe remainder of its deflection range in response to the change in thethermal conductivity of said atmosphere produced by a variation in itsCO2 content. i

2. Measuring means for determining the composition'of a controlledfurnace atmosphere containing gases formed by the more or less completecombustion of air and a fuel gas comprising in combination a measuringcircuit including test and standard cell resistors for creating apotential difference varying as the thermal conductivity of saidatmosphere is varied, and d8? fleeting means responsive to anddeflecting in accordance with said potential difference, and adjustmentmeans automatically actuated as said potential difference passes througha certain intermediate value to adjust said measuring means fordeflection of said element through approximately one half of itsdeflective range in response to the change in its thermal conductivityproduced by a variation inthe hydrogen content of said atmosphere fromzero to approximately 100%, or for deflection through substanin responseto the change in thermal conductivity produced by a variation in the CO2content from zero to 14%. i 3. Measuring means for determining thecomparison of a controlled furnace atmosphere formed by the gaseousresultant of the more or less complete combustion of air and a fuel gas,comprising in combination a measuring circuit including test andstandard cell resistors for creating a potential diiference varying inaccordance with changes in the thermal conductivity of said atmosphere,an element adapted to deflect in accordance with'changes in saidpotential difference, and adjustment means including a switch mechanismoperated by the deflection of said element through an intermediateportion of its range of deflection for adjusting said measuring meansinto oneor the other of two operating conditions, accordingly as saidelement moves in one direction or the other'through said intermediateposition, said measuring means being operable when in one of itsconditions, to effect deflection of said element through a substantialportion of its total range of deflection on a thermal conductivitychange corresponding to an increase in the CO2 content of saidatmosphere from zero to approximately 14% and being operable in thesecond of said conditions to effect deflections of said element throughsecond portion of its range of deflection of no greater extent than thefirst mentioned portion, as the hydrogen content of the atmosphereincreases from zero to a percentage substantially greater than 14%.

4. In a measuring instrument, the combina-' tion with a measuringcircuit comprising points having their relative. potentials varied by achange in the value of a quantity measured, mechanism responsive tovariations in the relaj tive potentials of said points and actuatedthereby to respond to variations in the quantity measured, of anexhibiting member moved by said mechanism progressively in one directionalong a path of deflection on a progressive variasaid quantity is below,or above, said intermediate value.

5. In a measuring instrument, the combination with a measuring circuitcomprising points having their relative potentials varied by a change inthe value of a quantity measured,

' mechanism responsive to variations in the relavary the ratio of themovement of said member to the change in said quantity, whereby themeasurements of said quantity are made to one scale, or to a secondscale, accordingly as the I value of said quantity is below, or above,said intermediate value.

6. In a measuring instrument, the combination with means for measuring avarying quantity, of

a member adapted to be moved by said means in tion of said quantity inone direction through a measurable range of variation, and meansactuated by said mechanism to adjustsaid measuring circuit as requiredto vary the ratio of the movement of said member to the change in saidquantity on the attainment by the latter of a certain intermediatevalue, whereby measurements of said quantityare made to one scale, or

to a second scale, accor ingly as the value of proportion to the changesin said quantity as the latter varies through a measurable range ofvariation, an exhibiting element, an operative connection between saidmember and said exhibiting element through which movements of saidmember gives movements to said exhibiting element, and means actuated bysaid first men-- tioned means to adjust said operative connection tomaintain different proportions between moveresistor resistance,comprising slide wire resistance means including a part adjustable torebalance' the potentiometer, a shaft rotatable in'correspondence withthe adjustments of said part, an element deflectedby the rotation ofsaid.

shaft to an extent and in a direction depending on the magnitude anddirection of rotation of the shaft, and adjusting means including anelectric switch mechanism actuated by the rotation of said shaft toincrease or decrease the magni-.

tude of the rebalancing adjustment of said part required to compensatefor a given change inthe thermal conductivity of the test cellatmosphereaccordingly as the latter conductivity is less than or exceeds apredetermined amount.'

8. In thermal conductivity measuring-appara-.

his the combination with a circuit network com prising comparison andtest gas cell resistors and H means for creating a current flow throughsaid resistors, of means for measuring the difference in potentialbetween points in said network, the relative potentials of which vary inresponse to changes in test cell resistor resistance, comprising agalvanometer connected to said network and deflecting in correspondencewith the changes in test cell resistor resistance, mechani-" two ways,by depression of the pointer when the latter moves in one direction orthe other through an intermediate portion of its range of deflection andmeans through which the actuation of said switch mechanism in onedirection or the other increases or decreases the extent of galvanometerdeflection produced by a given change in the thermal conductivity of theatmosphere in the test cell.

9. Apparatus for determining the thermal conductivity of a controlledfurnace atmosphere containing gases formed by the combustion of a fuelgas including carbon and hydrogen constituents, comprising an electriccircuit network including a resistor varying in resistance with thethermal conductivity of the atmosphere, means for creating an electriccurrent flow in said network, a deflecting element, means operativelyconnecting said element to said network to deflect in response tochanges in the resistance of said resistor, and adjusting means actuatedby the deflection of said element through an intermediate portion of itsrange of deflection for adjusting said apparatus to efiect a magnitudeof deflection of said element in response to a given extent of change inthe thermal conductivity of said atmosphere, which is greater in theportion of said range at one side than in the portion of said range atthe other side of said intermediate portion.

10. Apparatus for determining the thermal,

conductivity of the atmosphere which is sub-.

stantially greater when the atmosphere is in an oxidizing condition thanwhen it is in a reducing condition.

11. Apparatus for determining the thermal conductivity of a controlledfurnace atmosphere containing gases formed by the combustion of a fuelgas including carbon and hydrogen constituents', comprising an'electriccircuit network including a resistor varying in resistance with thethermal conductivity of the atmosphere, means for creating an electriccurrent flow in said network, a deflecting element, means operativelyconnecting said element to said network to deflect in response tochanges in the resistance of said resistor, and adjusting means actuatedby the deflection of said element to adjust said apparatus for amagnitude of deflection of said element in response to a given extent ofchange in the thermal conductivity of said atmosphere which is greaterin the portion of the range of deflection of said element in which thethermal conductivity of said atmosphere is primarily dependent on itsCO2 content, than in the range portion in which the thermal conductivityof the atmosphere is primarily dependent on its H2 content.

12. In thermal conductivity measuring apparatus, the combination with acircuit network comprising comparison and test gas cell resistors andmeans for creating a current flow through said resistors, of aself-balancing potentiometer for measuring the difference in potentialbetween points in said network, the relative potentials of which vary inresponse to changes in test cell resistor resistance, comprising slidewire resistance means including a part adjustable to rebalance saidpotentiometer, a deflecting element, a mechanical connection betweensaid part and element adjustable to vary the extent of elementdeflection produced by a given adjustment of said part, said mechanicalconnection including a shaft rotatable to effect the deflection of saidelement, and means actuated by said shaft to an extent and in adirection depending on its rotation to adjust said mechanical connectionas the thermal conductivity of the test cell atmosphere varies through acertain intermediate value, to increase or decrease the extent ofelement deflection produced by a given change in the thermalconductivity of the test cell atmosphere, when said conductivity is lessthan or exceeds a predetermined amount.

13. Apparatus for determining the composition of a controlled furnaceatmosphere containing gases formed by the more or less completecombustion of air and a fuel gas, comprising in combination with meansincluding test and standard cells for creating a potential differencevarying as the thermal conductivity of said atmosphere is varied, adeflectaible element, associated measuring means responsive to saidpotential difference for causing said element to deflect in accordancewith changes in said thermal conductivity and including adjustment meansauto-- matically actuated as said potential difference attains a.certain intermediate value, to adjust said apparatus for deflection ofsaid element through a substantial portion of its deflective range inresponse to the change in the thermal conductivity of said atmosphereproduced by a variation in its hydrogen content and for deflection ofsaid element through substantially all of the remainder of itsdeflection range in response to the change in the thermal conductivityof said atmosphere produced by a variation in its CO2 content.

ANKER E. KROGH. JOSEPH P. VOLLRATH.

